This invention relates in general to coating compositions and in particular to a new and useful decorative black wear protection coating.
The blackening of metal objects by substoichiometric oxide coatings is a process long known. Thus, for example cutting tools of high-speed steel are "drawn" by means of steam, i.e. they are subjected to oxidation in a very thin zone near its surface. The black oxide layer thus produced sometimes increases the wear resistance somewhat, in that it reduces the so-called adhesion wear. Additional similar methods are known, which in part are combined with phosphatizing. As the specialist knows, all these known methods lead to coatings which, though suitable for purely decorative purposes, are not suitable for real wear protection; they have too little resistance both to chemical attack and to mechanical abrasion. These methods, therefore, have hardly been used anymore for decades. Also the so-called black eloxizing falls in this category. The black decorative wear protection coatings common today are produced by electro-plating and are usually black chrome or black nickel coatings, that is, cermets (mixtures of metal with ceramic material) of the respective metals with their oxides, which due to their low light dispersion create the impression of black coloration. Such coatings still have, as is known, great deficiencies with regard to wear resistance, surface quality and skin compatibility.
It is known also that with titanium compounds one can obtain coatings of different coloration, from golden yellow titanium nitride and aubergine colored to brown carbonitrides to the blue oxides of so-called Magnelli phases. Characteristic of all these coatings is their diversity of color. It has, however, not been possible until now to produce black layers on this basis; only light gray films could at best be produced (with carbides).
Lastly it was known also to apply decorative carbon layers on objects, in that carbon was precipitated by cathode sputtering as a relatively loose film on the surfaces of the objects. These films were better than the films, also long known, which were obtained by vapor deposition of metals, e.g. platinum, in a residual gas greatly dispersing the vaporized molecules, and which also appeared black because of their structure with many cavities (porosity). But because of their insufficeint mechanical resistance for applications where relatively high mechanical stress during the period of use must be expected, in particular for applications as objects of daily use, none of the known black coatings constituted a real solution.